Development of Mouse Chow to Reflect Human Diet for Nutrition Intervention Studies

Current Developments in Nutrition · 2025-05-01

Regulation of glial ApoE secretion by the mevalonate pathway is independent of ApoE isoform

Journal of Alzheimer s Disease · 2025-02-24

BackgroundLipids synthesized in astrocytes are distributed to other brain cells in high-density lipoprotein-like ApoE particles. ApoE, which is a powerful genetic risk factor for developing Alzheimer's disease, is secreted differently depending on genotype. Secretion of ApoE from mouse astrocytes is regulated by the mevalonate pathway.ObjectiveWe aimed to understand if the regulation of ApoE secretion from astrocytes by the mevalonate pathway was the same between mouse ApoE and ApoE from humanized mice, and if this is impacted by ApoE isoform.MethodsAstrocyte-enriched glial cultures from wild-type and humanized ApoE targeted-replacement mice were treated with pharmacological inhibitors of various steps along the mevalonate pathway and ApoE in the conditioned media was measured.ResultsWe show that statins and prenylation inhibitors, but not specific cholesterol inhibitors, reduce extracellular ApoE lipoparticle levels in astrocyte-enriched glial cultures, and that this occurs in cells harboring either the mouse ApoE or any of the three human ApoE genotypes to a similar extent. We find that geranylgeranylation modulates ApoE release from astrocytes, and it does so independent of ApoE genotype.ConclusionsOur results suggest that prenylation broadly regulates ApoE secretion from astrocytes regardless of ApoE genotype, and that this is mediated specifically by geranylgeranylation. Therefore, our data implicates geranylgeranylation as a general mechanism modulating ApoE release from astrocytes, but likely is not responsible for the reported baseline differences in ApoE secretion seen in vivo and in vitro across genotypes.

7-ketocholesterol contributes to microglia-driven increases in astrocyte reactive oxygen species in Alzheimer’s disease

bioRxiv (Cold Spring Harbor Laboratory) · 2025-01-19 · 2 citations

Abstract Oxidative stress is a prominent feature of Alzheimer’s disease. Within this context, cholesterol undergoes oxidation, producing the pro-inflammatory product 7-ketocholesterol (7-KC). In this study, we observe elevated levels of 7-KC in the brains of the 3xTg mouse model of AD. To further understand the contribution of 7-KC on the oxidative environment, we developed a method to express a genetically encoded fluorescent hydrogen peroxide (H 2 O 2 ) sensor in astrocytes, the primary source of cholesterol in the brain. With this sensor, we discovered that 7-KC increases H 2 O 2 levels in astrocytes in vivo, but not when directly applied to astrocytes in vitro. Interestingly, when 7-KC was applied to a microglia cell line alone or mixed astrocyte and microglia cultures, it resulted in microglia activation and increased oxidative stress in astrocytes. Depletion of microglia from 3xTg mice resulted in reduced 7-KC in the brains of these mice. Taken together, these findings suggest that 7-KC, acting through microglia, contributes to increased astrocyte oxidative stress in AD. This study sheds light on the complex interplay between cholesterol oxidation, microglia activation, and astrocyte oxidative stress in the pathogenesis of AD.

Author Response: Mechanical activation of TWIK-related potassium channel by nanoscopic movement and rapid second messenger signaling

2024-02-26

“Ouch!”: you have just stabbed your little toe on the sharp corner of a coffee table. That painful sensation stems from nerve cells converting information about external forces into electric signals the brain can interpret. Increasingly, new evidence is suggesting that this process may be starting at fat-based structures within the membrane of these cells. The cell membrane is formed of two interconnected, flexible sheets of lipids in which embedded structures or molecules are free to move. This organisation allows the membrane to physically respond to external forces and, in turn, to set in motion chains of molecular events that help fine-tune how cells relay such information to the brain. For instance, an enzyme known as PLD2 is bound to lipid rafts – precisely arranged, rigid fatty ‘clumps’ in the membrane that are partly formed of cholesterol. PLD2 has also been shown to physically interact with and then activate the ion channel TREK-1, a membrane-based protein that helps to prevent nerve cells from relaying pain signals. However, the exact mechanism underpinning these interactions is difficult to study due to the nature and size of the molecules involved. To address this question, Petersen et al. combined a technology called super-resolution imaging with a new approach that allowed them to observe how membrane lipids respond to pressure and fluid shear. The experiments showed that mechanical forces disrupt the careful arrangement of lipid rafts, causing PLD2 and TREK-1 to be released. They can then move through the surrounding membrane where they reach a switch that turns on TREK-1. Further work revealed that the levels of cholesterol available to mouse cells directly influenced how the clumps could form and bind to PLD2, and in turn, dialled up and down the protective signal mediated by TREK-1. Overall, the study by Petersen et al. shows that the membrane of nerve cells can contain cholesterol-based ‘fat sensors’ that help to detect external forces and participate in pain regulation. By dissecting these processes, it may be possible to better understand and treat conditions such as diabetes and lupus, which are associated with both pain sensitivity and elevated levels of cholesterol in tissues.

Mechanical activation of TWIK-related potassium channel by nanoscopic movement and rapid second messenger signaling

eLife · 2024-02-26 · 5 citations

Rapid conversion of force into a biological signal enables living cells to respond to mechanical forces in their environment. The force is believed to initially affect the plasma membrane and then alter the behavior of membrane proteins. Phospholipase D2 (PLD2) is a mechanosensitive enzyme that is regulated by a structured membrane-lipid site comprised of cholesterol and saturated ganglioside (GM1). Here we show stretch activation of TWIK-related K + channel (TREK-1) is mechanically evoked by PLD2 and spatial patterning involving ordered GM1 and 4,5-bisphosphate (PIP 2 ) clusters in mammalian cells. First, mechanical force deforms the ordered lipids, which disrupts the interaction of PLD2 with the GM1 lipids and allows a complex of TREK-1 and PLD2 to associate with PIP 2 clusters. The association with PIP 2 activates the enzyme, which produces the second messenger phosphatidic acid (PA) that gates the channel. Co-expression of catalytically inactive PLD2 inhibits TREK-1 stretch currents in a biological membrane. Cellular uptake of cholesterol inhibits TREK-1 currents in culture and depletion of cholesterol from astrocytes releases TREK-1 from GM1 lipids in mouse brain. Depletion of the PLD2 ortholog in flies results in hypersensitivity to mechanical force. We conclude PLD2 mechanosensitivity combines with TREK-1 ion permeability to elicit a mechanically evoked response.

Combined effects of genetic background and diet on mouse metabolism and gene expression

iScience · 2024-11-04 · 3 citations

In humans, dietary patterns impact weight and metabolism differentially across individuals. To uncover genetic determinants for differential dietary effects, we subjected four genetically diverse mouse strains to humanized diets (American, Mediterranean, vegetarian, and vegan) with similar macronutrient composition, and performed body weight, metabolic parameter, and RNA-seq analysis. We observed pronounced diet- and strain-dependent effects on weight, and triglyceride and insulin levels. Differences in fat mass, adipose tissue, and skeletal muscle glucose uptake, and gene expression changes in most tissues were strain-dependent. In visceral adipose tissue, ∼400 genes responded to diet in a strain-dependent manner, many of them in metabolite transport and lipid metabolism pathways and several previously identified to modify diet effects in humans. Thus, genetic background profoundly impacts metabolism, though chosen dietary patterns modify the strong genetic effects. This study paves the way for future mechanistic investigations into strain-diet interactions in mice and translation to precision nutrition in humans.

Reviewer #2 (Public Review): Mechanical activation of TWIK-related potassium channel by nanoscopic movement and rapid second messenger signaling

2023-12-19

Rapid conversion of force into a biological signal enables living cells to respond to mechanical forces in their environment. The force is believed to initially affect the plasma membrane and then alter the behavior of membrane proteins. Phospholipase D2 (PLD2) is a mechanosensitive enzyme that is regulated by a structured membrane-lipid site comprised of cholesterol and saturated ganglioside (GM1). Here we show stretch activation of TWIK-related K+ channel (TREK-1) is mechanically evoked by PLD2 and spatial patterning involving ordered GM1 and 4,5-bisphosphate (PIP2) clusters. First, mechanical force deforms the ordered lipids, which lowers membrane cholesterol, disrupts the interaction of PLD2 with the GM1 lipids, and allows a complex of TREK-1 and PLD2 to associate with PIP2 clusters. The association with PIP2 activates the enzyme, which produces the second messenger phosphatidic acid (PA) that gates the channel. Co-expression of catalytically inactive PLD2 inhibits TREK-1 stretch currents in a biological membrane. Cellular uptake of cholesterol inhibits TREK-1 currents in culture and depletion of cholesterol from astrocytes releases TREK-1 from GM1 lipids in mouse brain. Depletion of the PLD2 ortholog in flies results in hypersensitivity to mechanical force. We conclude PLD2 mechanosensitivity combines with TREK-1 ion permeability to elicit a mechanically evoked response.Shear thinning activates TREK-1 through a second messenger.

List of contributors

Insulin · 2023-01-01

Author Response: Mechanical activation of TWIK-related potassium channel by nanoscopic movement and rapid second messenger signaling

2023-12-19

Rapid conversion of force into a biological signal enables living cells to respond to mechanical forces in their environment. The force is believed to initially affect the plasma membrane and then alter the behavior of membrane proteins. Phospholipase D2 (PLD2) is a mechanosensitive enzyme that is regulated by a structured membrane-lipid site comprised of cholesterol and saturated ganglioside (GM1). Here we show stretch activation of TWIK-related K+ channel (TREK-1) is mechanically evoked by PLD2 and spatial patterning involving ordered GM1 and 4,5-bisphosphate (PIP2) clusters. First, mechanical force deforms the ordered lipids, which lowers membrane cholesterol, disrupts the interaction of PLD2 with the GM1 lipids, and allows a complex of TREK-1 and PLD2 to associate with PIP2 clusters. The association with PIP2 activates the enzyme, which produces the second messenger phosphatidic acid (PA) that gates the channel. Co-expression of catalytically inactive PLD2 inhibits TREK-1 stretch currents in a biological membrane. Cellular uptake of cholesterol inhibits TREK-1 currents in culture and depletion of cholesterol from astrocytes releases TREK-1 from GM1 lipids in mouse brain. Depletion of the PLD2 ortholog in flies results in hypersensitivity to mechanical force. We conclude PLD2 mechanosensitivity combines with TREK-1 ion permeability to elicit a mechanically evoked response.Shear thinning activates TREK-1 through a second messenger.

Insulin and neurodegenerative diseases

Insulin · 2023-01-01